The present invention relates to a helicopter rotor.
In general, a helicopter rotor comprising a central, substantially plate-like hub having a polygonal outline is known; from such hub extend, radially outwardly, a plurality of blades uniformly distributed around a central axis of rotation of the rotor itself. Each of the said blades is normally connected to the hub by an attachment element or bracket a central portion of which extends through a respective axial aperture formed through the hub. The coupling between each attachment bracket and the hub is normally made by an elastomeric coupling interposed between the said central portion of the bracket and a bridging element extending along the periphery of the hub and delimiting the radially outer part of the said aperture.
Each of the elastomeric joints mentioned above permits an associated blade to perform relatively large oscillations about its centre which can be separated into components of vertical oscillation perpendicular to the plane of rotation, and horizontal oscillation coplanar with the rotor.
It is known to limit in any one case the amplitude of the said vertical oscillations by dynamic elements acting to prevent substantial upward and downward displacements during the acceleration and deceleration phases respectively. The said horizontal oscillations are, on the other hand, normally controlled by dampers which, in some particularly critical situations, have been found to be wholly inadequate These critical situations occur, in particular, upon take off when the ambient and atmospheric conditions are not favourable, for example gusts of cross winds upon take-off from the bridge of a ship. In this case the dampers normally utilised are not able to absorb the relatively high dynamic loading due to the inertial displacements of the blades with the risk that oscillatory strains of such violence can be transmitted to the rotor as not only to impede a normal take off, but also to cause the helicopter to capsize.
The use of more powerful dampers has been found to be inadvisable since although on the one hand these would improve the performance of the helicopter upon take off in critical conditions, on the other hand they would cause a deterioration in the performance thereof in normal operating conditions.